1. Field of the Invention
The present invention relates to a horizontal deflection apparatus which deflects an electron beam in a horizontal direction for scanning a picture tube, and more in particular, to an improvement of the art to correct a horizontal width and crosswise pincushion distortion of a screen in accordance with a plurality of horizontal and vertical frequencies.
2. Description of Related Art
There has conventionally been manufactured a display apparatus, in which each of the horizontal and vertical frequencies is adapted to correspond to a single frequency. FIG. 1 is a block diagram to illustrate the construction of a horizontal deflection apparatus used in the conventional display apparatus. In the figure, reference numeral 21 represents a monostable multivibrator driven in response to a horizontal synchronizing signal H, and an output pulse of this monostable multivibrator 21 is given to an integrator 22 in which the output pulse is smoothed to obtain an output voltage Vr. The output voltage Vr outputted from the integrator 22 is transmitted to a positive input terminal of an error amplifier 23, which is rendered a reference voltage for comparison with a feedback voltage inputted to a negative input terminal of the error amplifier 23 as will be described later. The negative input terminal of the error amplifier 23 is earthed via a resistance 26. An error output of the error amplifier 23 is given to a voltage stabilizing circuit 24 which outputs a stabilization voltage V.sub.B in accordance with the error output. While this stabilization voltage V.sub.B is fed back to the negative input terminal of the error amplifier 23 via a resistance 25, this is inputted as a power source to a horizontal output circuit 28 via a choke coil 27 which is comprised of a coil of a horizontal output transformer or the like. The horizontal output circuit 28 is well known as it consists of such elements as a horizontal output transistor 29, a damper diode 30, a resonance capacitor 31, a horizontal deflection coil 32, a crosswise pincushion distortion correcting transformer 33, an S distortion correcting capacitor 34, and the like.
Reference numeral 35 indicates an output terminal of a vertical deflection voltage V.sub.D which is outputted from a vertical output circuit (not shown), and the outputted vertical deflection voltage Vd is applied to a vertical deflection coil 36 which is comprised of a coil of a vertical output transformer or the like. Via the vertical deflection coil 36, the vertical deflection voltage V.sub.D is given to one electrode of a capacitor 37, and converted into a crosswise pincushion distortion correction voltage in the form of a parabola. While the other electrode of the capacitor 37 is connected to one end of a secondary coil of the correcting transformer 33, a +B power voltage inputted to a+B power terminal 38 is added thereto via a resistance 39. Between both ends of the secondary coil of the correcting transformer 33 are provided a vertical frequency resonance capacitor 40 and a resonance resistance 41.
Now the operation of the conventional horizontal deflection apparatus in the above construction will be described below.
When the horizontal synchronizing signal H is applied to the monostable multivibrator 21, a pseudo horizontal synchronizing signal is obtained which has a fixed pulse width irrespective of the horizontal frequency. And when this signal is passed through the integrator 22, there is obtained the voltage Vr which is proportional to the frequency of the horizontal synchronizing signal, that is, the horizontal frequency. With this voltage Vr as the reference voltage, the error amplifier 23 is actuated and its error output is fed back to the voltage stabilizing circuit 24.
Both the monostable multivibrator 21 and integrator 22 constitute a frequency-voltage conversion circuit which generates the reference voltage Vr corresponding to the horizontal frequency. In accordance with the change of the reference voltage Vr, the stabilization voltage V.sub.B outputted from the voltage stabilizing circuit 24 is changed, whereby, the value of a horizontal deflection current, that is, horizontal amplitude is maintained constant.
In order to correct a crosswise pincushion distortion of the screen, the vertical deflection voltage V.sub.D is converted into a correction voltage in the form of a parabola by the vertical deflection coil 36, capacitor 37, and the like, so that the amplitude of the above horizontal deflection current is modulated via a resonance circuit which is comprised of the correcting transformer 33, capacitor 40, resistance 41, and the like.
When the conventional horizontal deflection apparatus constructed in the above-described fashion is to correct the crosswise pincushion distortion, it employs the resonance circuit which is comprised of the correcting transformer 33, capacitor 40, and resistance 41 and which resonates at a fixed vertical frequency, and accordingly, the resonance circuit may not resonate, when the vertical frequency changes, resulting in such a problem that the crosswise pincushion distortion is not adequately corrected.